AB1237 COMPARISON BETWEEN ENZYME IMMUNOASSAY AND CHEMILUMINESCENCE TO DETERMINE THE CONCENTRATION OF SERUM CALPROTECTIN AND ITS ASSOCIATION WITH CLINICAL VARIABLES IN PEDIATRIC RHEUMATOLOGY.
Authors: H. Codes-Mendez, B. Magallares, L. Martínez-Martínez, H. Park, D. Lobo Prat, L. Sainz Comas, I. Gich, Y. Alvaro, E. Molto, V. Calahorro, S. Boronat, H. Corominas
Journal: Annals of the Rheumatic Diseases (2022)

Background Serum calprotectin (SC) is an emerging biomarker in the measurement of inflammation. It can be determined by different techniques, such as enzyme immunoassay (EIA) or chemiluminescence (CLIA). However, there are no studies comparing whether there is a correlation between the two diagnostic methods in paediatric rheumatologic diseases. Objectives (i) To assess whether there are differences between serum calprotectin (SC) levels determined by EIA (Bühlmann ) method and CLIA (QUANTA Flash ) in pediatric age patients with systemic autoimmune rheumatic disease (SARD). (ii) To evaluate which clinical and analytical variables are associated with an increase of SC in each method. Methods Analytical cross-sectional study that included patients from a pediatric rheumatology specialized unit between 02/2017 and 05/2021. We included 41 patients with SARD who had at least one SC analysis determined by EIA in their routine controls (144 serum) and afterwards had SC determined again, this time using the CLIA method. The collected variables were sex, age, remission according to clinical judgment, swollen joint count according to physical examination (PE Count) and ultrasound (US Count), Juvenile Arthritis Disease Activity Score according to physical examination (PE JADAS-27) and ultrasound (US JADAS-27), C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR). As for the statistical analysis, intraclass correlation (ICC) and paired samples t-test were performed to compare the two methods. Univariate linear regression was performed to study the association between EIA, CLIA and both clinical and analytical variables. Results We included 41 patients, 50.1% were women with a mean age (± SD) of 13.1 (± 3.8) years. The details of their descriptive characteristics were: mean SC (EIA) of 3.1 (±1.8) µg/ml, mean SC (CLIA) of 2.5 (±1.6) µg/ml, mean CRP of 2.6 (± 6.5) mg/l, mean ESR of 10.1 (± 11) mm/h, and mean PE JADAS-27 of 2.8 (± 8). Most frequent diagnosis was oligoarticular juvenile idiopathic arthritis (JIA) (24.4%), followed by enthesitis-related (ERA) JIA (12.2%) and polyarticular JIA (12.2%), familial Mediterranean fever (FMF) (9.8%), psoriatic JIA (4.9%), systemic JIA (4.9%) and syndrome of periodic fever, aphtous stomatitis, pharyngitis, and cervical adenitis (PFAPA) (4.9%), vasculitis (4.8%), and undifferentiated JIA (2.4%). Clinical diagnosis was unspecific in 9.8% of the patients. In our sample, 66.7% were in clinical remission at the discretion of the specialist. A statistically significant Pearson’s CCI of 0.77 (95%CI 0.70-0.83; p=0.00) was observed as a single measure between EIA and CLIA and with an average of 0.87 (95%CI=0.82-0.91; p=0.000). Figure 1 shows the dispersion of this correlation. On the other hand, we observed a statistically significant difference in the mean between both methods of 0.58 (95%CI=0.40-0.77; p=0.000), observing a greater difference in SC (EIA) &gt; 4 µg/ml. A significant association was observed between EIA and clinical remission, joint count, JADAS and CRP; and also between CLIA and clinical remission, JADAS and CRP. The analysis performed is shown in Table 1. Table 1. Association between EIA and CLIA with clinical and analytical variables. Remission PE Count US Count PE JADAS US JADAS b p b p b p b p b p SC(EIA) 0.43 0.011 0.14 0.027 0.08 0.024 0.09 0.000 0.06 0.000 SC(CLIA) 0.53 0.000 -0.00 0.945 0.31 0.320 0.05 0.021 0.04 0.015 Sex Gender ESR CRP b p b p b p b p SC(EIA) 0.00 0.997 0.05 0.207 0.00 0.487 0.05 0.027 SC(CLIA) -0.24 0.362 0.01 0.795 0.02 0.105 0.08 0.000 b, regression coefficient; p, statistical significance. Conclusion There is a good correlation between EIA and CLIA methods to determine SC in pediatric patients with SARD. Significant differences were observed between both methods above the value of 4 µg/ml. This fact could be explained by methodological differences, since CLIA discriminates better at higher values than EIA. An association was observed between both methods and variables of remission or disease activity. Disclosure of Interests None declared